Compositions for foundry molding processes utilizing reclaimed sand

ABSTRACT

The present invention provides a binder solution having a low solids level which provides improved tensile properties when used with reclaimed sand. This binder solution comprises an alkaline phenolic resin which is cured at ambient temperature with an ester-functional curing agent. Also provided by this invention are raw batch formulations comprising sand, a binder solution having a low solids level, and a curing agent. These raw batch formulations include embodiments wherein the low solids levels are obtained by the separate addition of a solvent. The methods for producing foundry molds and cores of this invention included those procedures wherein dilution water is used to reduce the solids contents of conventional, relatively high solids content binder solutions.

This is a divisional of application Ser. No. 568,630, filed Aug. 16,1990, now U.S. Pat. No. 5,082,876, which was a continuation of Ser. No.179,391 filed Apr. 8, 1988, and now abandoned.

FIELD OF THE INVENTION

This invention relates to the manufacture of articles such as foundrymolds and cores made from sand that is mixed with an alkaline phenolicresin binder, where the sand comprises a high level of reclaimed sand.More particularly, a portion of this invention relates to novel binderssolutions for use with reclaimed sand, which binder solutions providehigher tensile strengths for articles produced therefrom.

RELATED APPLICATION

This application is closely related to a companion application Ser. No.596,546, filed Oct. 12, 1990, now U.S. Pat. No. 5,089,540, which was acontinuation-in-part of Ser. No. 538,588, filed Jun. 15, 1990 which, wasa continuation of Ser. No. 179,392, filed Apr. 8, 1988, and nowabandoned.

BACKGROUND OF THE INVENTION

In the manufacture of foundry molds and cores from sand using a curablebinder, recycling the sand is an important economic consideration.Foundry sand can normally be used, then reused, repeatedly, when mostresin binders are used. Normally there is a small loss of sand on reuse,and this loss is made up by adding pristine sand to the used sand. Theseconditions are experienced with most resin binders.

In recent years, however, ester cured alkaline phenolic resins have goneinto widespread use. These resins can be ester cured at ambienttemperature. Such resin binder systems are disclosed, for example, inpatents: U.S. Pat. No. 4,426,467, in which lactones are used as thecuring agents; U.S. Pat. No. 4,474,904, in which esters are so used; andU.S. Pat. No. 4,468,359, in which the esters are in the gaseous or vaporphase.

While these binding systems offer many advantages, there are offsettingdisadvantages that are sometimes observed. For example when the sand isreused, the tensile strength of the molds or cores drops off. This mayhave a serious effect on the economics of the foundry.

The extent to which previously used sand is able to be reused is oftendetermined by the tensile properties that can be achieved. One factorwhich determines the tensile strength is the ability of the binder tobond to the surfaces of the reclaimed sand. Higher rebonding strengthsallow higher usage levels of reclaimed sand.

Sand reclamation is the physical, chemical or thermal treatment of arefractory aggregate to allow its reuse. Ideally there is no significantloss of its original useful properties as required for the applicationinvolved.

In typical foundry operations, the sand is collected after taking out acasting from a poured mold. This sand comprises loose sand grains, sandagglomerates and lumps of bonded sand. All these are broken down bymechanical devices into free-flowing granules. These granules arescreened to produce reclaimed sand, ready for reuse. This is thesimplest form of sand reclamation. The reclaimed sand from this processgenerally has layers of burned and partially burned binder films stilladhering to it. The amount of such organic layer present can bedetermined by a loss-on-ignition (L.O.I.) determination.

The granular sand can be further processed to remove the binder residuelayer either by mechanical means (sand scrubbers) or thermal means (arotary kiln). The reclaimed sand that has been subjected to theseadditional processes is characterized by low LOI values as compared tothe simple granular sand described above, as it comes from a used moldor core.

Pristine foundry sand would normally have negligible LOI and aparticular, specified screen distribution (AFS Handbook). Idealreclamation would return used sand to its original LOI and screendistribution values.

There are thus three treatments available for reclaiming sand. Theseinclude mechanical, wet, and thermal treatment processes. The mechanicaltreatment process typically involve subjecting the sand granules togrinding, scrubbing or other means of mechanical attrition to provideparticles of a desired size, remove binder residues, provide new sandsurfaces and/or remove fines. The equipment and process used may dependon the particle size and uniformity desired. The wet treatment processesinvolve washing the sand granules with water, draining the wash waterand drying the washed sand. In thermal treatment processes, the sand isheated to a temperature of about 120° C. or above, wherein the binderresidue is decomposed or burned.

The mechanical treatment processes and thermal treatment processes havenot proven very effective in enhancing the bonding properties ofreclaimed sand obtained from foundry cores and molds wherein the binderis an ester cured alkaline phenolic resin. Such sand is characterized bybinder film residues or the sand surfaces, whose presence is indicted bymany resulting properties, including a residual alkalinity. Theseresidues may be the cause of the poor bonding characteristics of thereclaimed sand when reused with an ester cured alkaline phenolic resinbinder. Wet treatment processes have been found to increase the bondingstrength of such reclaimed sand, but are expensive, consume energy, andentail a disposal problem. It is believed the wet treatment processes"cleanse" the surface of the sand of at least some harmful residues,whereas the mechanical and thermal treatment processes are not aseffective.

Most foundries utilize a simple mechanical treatment in reclaiming sand,and avoid the environmental problems of wet treatment and theexpenditures of energy required for thermal treatment. These foundriescompensate for the loss in bonding properties by mixing the reclaimedsand with pristine sand. The usage level of mechanically treated,thermally treated or untreated reclaimed sand may only be about 50weight percent of the total sand used. There is an economic incentive,as well as environmental and other incentives, to enhance the usagelevel of such reclaimed sand.

In comparison, sand recovered from foundry molds and cores: which employan acid cured binder, such as acid cured phenolic resins, acid curedfuran resin, and phenolic-urethane resins, generally show no significantloss in bonding strength after thermal or mechanical treatment, ascompared to pristine sand. When reclaimed sand shows no loss in bondingability, generally its reuse can be as high as 80% to 90% by weight ofthe total sand used. Theoretically, the usage level of such reclaimedsand can be as high as 100%; however, there are usually losses infoundry operations due to spillage and other handling losses. Therefore,it is necessary to replenish the stock of sand with pristine sand.

It is desirable to enhance the bonding affinity and ability of usedsand, reclaimed from foundry use, that has been bonded with an estercured alkaline phenolic resin, particularly a highly alkaline phenolicresin, to the extent that usage levels of such reclaimed sand may be ashigh as 60% to 80% or 90% by weight in subsequent foundry operations.

Solutions of alkaline phenolic resins that are curable with curingagents having ester functionality have been disclosed in U.S. Pat. Nos.4,426,467, 4,468,359 and 4,474,904, as mentioned above. In U.S. Pat. No.4,426,467, the curing agents are lactones, which are self condensedcyclic esters, and the resin binder solutions have preferred solidscontents in the range from 80% to 95% by weight. Suitable solidsconcentrations are said to be in the range from 60% to 95% by weight.The solutions of curable resin binders disclosed in U.S. Pat. Nos.4,468,359 and 4,474,904 have solids contents falling within the range of50% to 75% by weight. These three U.S. Patents are expresslyincorporated herein by reference.

Resin solutions with lower solids contents in the range from 40% to 70%by weight have been disclosed in Japanese Laid Open Patent ApplicationNo. 62-282743, assigned to Dainippon Ink. However, the resin solids inthese solutions are augmented with added resin solids prior to use.These added resin solids are dissolved in the organic ester curing agentin an amount of from 20% to 60% by weight, based on the weight of theester.

It is recognized in the art that the tensile strengths of the finishedproducts suffer when the solids content of the binder solution fallsbelow about 50% by weight, when used with pristine sand.

SUMMARY OF THE INVENTION

It has now been discovered that solutions of alkaline phenolic resinswith solids in the range from about 33% to about 47% provide superiorbonding properties for used, reclaimed sand, when compared to thoseobtained by the use of similar resin binder solutions at conventional,higher solids contents, and that said lower solids content resinsolutions achieve higher tensile strengths for resin-bonded sandarticles such as foundry molds or cores made from reclaimed sand.

U.S. Pat. Nos. 4,474,904, 4,468,359, and 4,426,467 specified severalfeatures of their respective resin binders that were deemed necessaryfor their successful usage in the foundry, including relatively highsolids conetnes, i.e., above 50%.

The present invention resides in the use of solutions of alkalinephenolic resin binders, that are curable by curing agents having esterfunctionality, for binding sand of which at least 40% by weight, andpreferably from 50% to 100% by weight, and more preferably at least 60%to about 80% by weight, comprises reclaimed used sand, such as sand thathas been recovered from dismantled foundry molds or cores, andreclaimed. The invention is useful for used sand that has been reclaimedand has "residual alkalinity", as described below.

The resin binder solutions of this invention comprise from about 33% upto about 47% by weight solids, based on the weight of solution,preferably about 35% to about 45%, and most preferably, about 38% to42%. That is, the resin binder solutions that are useful in the practiceof this invention have solids contents of from about 33% to about 47%,and preferably, from about 35% to about 45%. The solids contents aredetermined by heating a 1.5 g sample at 135° C. for three hours, thedetermining weight of the remainder. The weight of the remainder isreported as the solids content. This procedure for determining thesolids content was used for all such determinations reported in thisapplication. The binder solutions of the invention generally haveBrookfield viscosity values of from 15 cps to 150 cps, as determinedutilizing a Model RVF Brookfield viscometer with a No. 1 spindle at 20rpm and at 25° C. These solids comprise an alkaline phenolic resin thatcan cure at room temperature with a curing agent having esterfunctionality.

Also provided by this invention is a raw batch composition whichcomprises a binder solution, a curing agent, and sand in substantiallyuniform admixture. This raw batch composition is useful for forming sandaggregates such as foundry molds and cores. The sand used comprises atleast 40% by weight sand which has been reclaimed from one or moremechanically dismantled foundry cores or molds. The "effective" solidscontent of the binder solution in the raw batch formulation is fromabout 33% to about 47% by weight, based on the weight of said solution.This "effective solids" content is achieved by the use of the bindersolutions of the present invention or by the use of a more concentratedbinder solution (i.e. one having a higher solids content than 33% up to47%) with dilution water, when forming the raw batch formulation.

In addition, a process is provided for using the raw batch formulationsof the present invention to form foundry molds or cores. In thisprocess, a raw batch formulation, as described above, is shaped into theconfiguration desired. The binder is then allowed to cure. The phenolicresin may be an alkaline phenolic resin, in which case a curing agentwith ester functionality will initiate curing under ambient conditions.Alternatively, if the phenolic resin is neutral or acidic, then thecuring agent should be a mixture or solution having ester functionalityand the ability to impart sufficient alkalinity to the resin uponadmixture with it to bring about curing conditions. The embodiments ofthis process also include shaping a mixture of sand and binder solution,and gassing this mixture with an ester-functional curing agent in vaporor gaseous form, to cure the resin.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates in one preferred embodiment to the use ofalkaline phenolic resin binders having relatively low solids contents,for forming foundry molds and cores from reclaimed sand.

The term "reclaimed sand" as used herein, refers to sand that has beenformed into a resin-bonded shape with an alkaline resin binder, thenrecovered for reclamation and reuse in the form of free flowing sandgranules. These free-flowing granules have residues of the alkalinebinder that are adhered to their surfaces.

The invention was developed for use with used sand that had beenpreviously bonded with an ester cured alkaline phenolic binder. Suchpreviously bonded sand, when recovered for reclamation, can be usedagain as is with an ester curable alkaline phenolic resin binder, butthe resin-bonded articles thus formed generally are characterized bytensile strengths that are lower than is desirable. This is believed tobe caused by the presence, on the used sand grains, of a water removableresidue. This residue appears to consist of several differentcomponents, but the important one with respect to effect on tensilestrength is believed to be an alkali silicate. If the alkaline phenolicresin binder previously used was a potassium phenolic resin, the residuewould comprise potassium silicate. Other alkaline silicates are believedto be produced by other alkaline resins.

While the identity of the residues, which are believed to be on thesurfaces of the sand grains, is not known with certainty, the presentinvention provides a practical means for using recovered used sand withan ester curable alkaline phenolic resin to form resin-bonded sandshapes having acceptable tensile strengths, despite the presence of suchresidues. The invention appears deceptively simple when known, but wasnot easy of development: it involves the use of ester curable alkalinephenolic resin binders in aqueous solutions at low solids contents,i.e., from about 33% to about 47%, and preferably from about 35% toabout 45% by weight. For convenient reference hereafter, the recoveredused sand, to which the invention is applicable, is referred to as sandrecovered from a shape previously bonded with an alkaline binder, or assand granules, having residual alkalinity, or as sand having on itssurfaces a water-removable residue. It is also believed that at least apart of the residue on the surfaces of the sand is alkaline silicatematerial. Consequently the reclaimed sand could also be referred to assand having on its surfaces residues comprising an alkaline silicate.These alternative expressions are apt because of uncertainty of thecause of the poor tensiles that are observed with recovered, previouslyalkaline-resin-bonded sand, although there is no uncertainty about theimprovement in tensiles obtained through the use of the presentinvention.

Recovered used sand may be prepared for use in the practice of theinvention by mechanical and thermal reclamation processes, as now knownin the art. Such processes can be used to produce reclaimed sandgranules of a size corresponding to a screen distribution of about25-140, as defined in the American Foundrymen Society's Handbook, "Moldsand Cores", pp. 4.2-4.5. A vibratory mill is typically the mechanicalmeans used to form the free flowing sand granules following shake-out ofthe loose sand from a mold.

Foundry sand or other refractory materials used in the production offoundry molds and cores is generally silica sand, quartz, chromite sand,zircon sand, or olivine sand, and may be beach sand, lake sand, banksand, but many other such materials could be used.

It is important to identify the binder residues that may be present onthe reclaimed sand to determine which reclamation and subsequent useprocesses will provide the best results. Binder residues that appear tohave a deleterious effect on the affinity of reclaimed sand, for aphenolic resin binder in particular, are those derived from binderscomprised of ester cured alkaline phenolic resins applied in aqueoussolutions. Such binders are often hardened with curing agents that haveester-functionality, which are referred to herein as "ester curingagents". Specific examples of "ester curing agents" are described moreparticularly below. Where these curing agents are used, the bindertypically hardens and cures under ambient conditions.

The recovered used sand, with which the invention is concerned, is sandthat has been previously bonded with a phenolic resin obtained by thereaction of a phenol such as phenol, cresols, resorcinol, 3,5-xylenol,bisphenol-A, other substituted phenols, or mixtures thereof, withaldehydes such as formaldehyde, acetaldehyde or furfuraldehyde.Preferred reactants are phenol and formaldehyde utilized in a molarratio of phenol to formaldehyde in the range of about 1:1 to about 1:3and more preferably 1:1.5 to 1:2.8.

Preferred alkaline materials used to condense these phenolic resinsinclude sodium hydroxide, potassium hydroxide, lithium hydroxide, andmixtures thereof, with potassium hydroxide being the most preferred. Apart of the alkaline material may be provided by substituting for a partof the alkali metal hydroxide a divalent metal hydroxide such as, forexample, magnesium hydroxide and calcium hydroxide. The preferredalkaline phenolic resins have an alkali:phenol molar ratio in the rangeof 0.2:1 to 1.2:1.

The more commonly used alkaline phenolic resin binders will have aBrookfield viscosity of from 75 to 250 cps, at a concentration of 53% to58% in water, utilizing a model RVF Brookfield viscometer with a No. 1spindle at 20 rpm and at 25° C. The binder solutions of this inventionhave solids contents of about 33% to about 47% by weight, preferably byabout 35% to 45% by weight, and most preferably, about 38% to about 42%by weight.

Suitable phenolic resins generally have a weight average molecularweight greater than about 500 and less than about 2500, more preferablygreater than about 1000, and most preferably within the range of about1000 to 2000, as determined by gel permeation chromatography (GPC). Inthe preferred GPC method, used herein, the resin sample is dissolved intetrahydrofuran (THF), then neutralized with 1N hydrochloric acid. Thesalt thus formed is removed by filtration, and the filtered supernatantliquid resin solution is run on a GPC apparatus to determine Mw. Theapparatus included a Waters model 6000A pump, a Waters model R401differential refractive index detector, a Waters model 730 Data Module,PL Gel 30 am 10 μ columns, porosities 10⁴, 500 and 50 Argstrom units,respectively, and a Rheodyne model 70-10 sample loop injector fittedwith a 100 μl loop and a 0.5 μm in-line filter situated between theinjector and the first column.

To determine Mw for an aqueous alkaline resole, the procedure is asfollows.

Dissolve 1 g resin in 10 ml methanol. Adjust the pH to 7 on a bufferedpH meter using IN hydrocholoric acid. Ad 10 ml unstabilized THF andcontinue stirring to ensure all the resin is in solution. Allow anyprecipitated salt to settle and transfer 500 μl of the supernatentliquor to a 5 ml sample vial. Remove the solvent under vacuum for theminimum of time (about 5 mins) and at a temperature of 35° C. Add 1 mlmobile phase and filter.

Primary calibration of the columns is carried out using phenol and theoligomers formed by reaction of 2,4'-dihydroxy diphenyl methane withformaldehyde at a mol. ratio of 1-5:1 with sulphuric acid catalys and atemperature of 120° C. for 30 mins. This gives individual peaks for upto 8-ring compounds (m.wt. 850). Above this the calibration curve isextrapolated.

Once the columns are calibrated with primary standards, resins may berun and their weight average molecular weights obtained. One of thesesamples may be chosen as a secondary standard to check the day-to-daytie-up not only of retention times but of calculated molecular weightaverages.

A standard resin solution should be injected each time the GPC system isstarted up and repeated until consistent retention times and molecularweights are obtained. If the calibration is satisfactory then samplesmay be run. If the results are consistent but vary from those expected,and there are no leaks or trapped air bubbles in the system, then thecolumns should be recalibrated with primary standards.

Some of the preferred phenolic resins used in the binder solution ofthis invention are the highly alkaline phenolic resins such as thosedescribed in U.S. Pat. Nos. 4,474,904 and 4,468,359. It is noted that inthese patents, the alkalinity content of the resins is expressed interms of the molar ratio of potassium hydroxide to phenol and thatpotassium hydroxide is described as the most preferred alkali. The molarratio of KOH:phenol for the preferred potassium alkaline resins for usein the practice of this invention falls in the range of about 0.2:1 toabout 1.2:1.

The binder solution useful in the practice of this invention preferablyis an aqueous solution of an alkaline phenol formaldehyde resin wherein

(i) the solids content is in the range from about 33% to about 47%,preferably 35% to 45%, and more preferably 38% to 42%,

(ii) the weight average molecular weight (Mw) is from 500 to 2500,preferably 700 to 2000, and more preferably 800 to 1700,

(iii) the formaldehyde:phenol molar ratio is from 1:1 to 3:1, preferably1.2:1 to 2.6:1,

(iv) the alkali:phenol molar ratio is from 0.2:1 to 1.2:1, preferably0.6:1 to 1.2:1,

(v) the alkali used comprises sodium hydroxide, potassium hydroxide, andtheir mixtures,

(vi) said solution may optionally contain a silane to the extent of0.05% to 3.0% by weight of said aqueous resin solution, and

(vii) said resin is curable at room temperature with C₁ -C₃ alkylformates, organic esters formed from C₁ -C₁₀ carboxylic acids and mono-and polyhydric alcohols and low molecular weight lactones includingbutyrolactone, propiolactone, caprolactone, and mixtures thereof.

However, the phenolic resin may also be an acidic or neutral resin, theaqueous solution of which is made alkaline either before or at the sametime that the ester-functional curing agent is added to the resinsolution. Otherwise, the parameter values (i) through (iii) and (vi)through (vii) apply, and after addition of the source of alkalinity tothe resin, the parameter values (iv) and (v) also apply, for the morepreferred embodiments.

Where the binder solution includes a silane, added for the purpose ofimproving the tensile strength of the molds or cores produced therefrom,the silane concentration may be as low as 0.05% by weight, based on theweight of the binder solution. Higher concentrations of silane providegreater improvements in strength up to quantities of about 0.6% byweight, based on the weight of the binder solution. The use of silaneconcentrations at higher levels, while useful, is not preferred becauseof the added cost. In addition, because one preferred silane often usedis an aminoalkyl alkoxy silane, which contains nitrogen, the use ofexcess silane may increase the risk of pinhole defects in the castingand for this reason, amounts in excess of 3% by weight, based on theweight of binder solution, are not used.

A silane, if used, is generally effective in increasing the tensilestrength of the foundry mold or core product. Suitable silanes includethose conforming to the formula R'Si(OR)_(n), wherein R' is a C₂ -C₆alkylene group, bonded to an amino, epoxy, mercapto, glycidoxy, ureido,hydroxy, hydroxy-C₁ -C₆, alkyl amino, amino-C₁ -C₆ alkyl amino, C₂ -C₆alkenyl or C₂ -C₆ alkenyl-carboxy group, and the groups R may be thesame or different and are selected from C₁ -C₆ alkyl and C₁ -C₆ alkoxysubstituted C₁ -C₆ alkyl groups.

Also included are those aminoalkyl alkoxy silanes which conform to thegeneral formula

    H.sub.2 N(CH.sub.2).sub.n Si(OR.sup.1).sub.3-x (R.sup.2).sub.x,

wherein n equals a whole number of from 2-4, R¹ is an alkyl group offrom 1-4 carbon atoms and phenyl, R² is an alkyl group of 1-4 carbonatoms and x is 0 or 1. Specific examples of such silanes which conformedto either or the above formulas include:

gamma-aminopropyl trimethoxysilane,

gamma-aminopropyl triethoxysilane (Silane A-1100)

gamma-aminobutyl triethoxysilane,

gamma-aminopentyl triethoxysilane,

gamma-aminopropyl diethoxymethylsilane,

gamma-aminopropyl diethoxyethylsilane,

gamma-aminopropyl diethoxyphenylsilane,

delta-aminobutyl diethoxyphenylsilane,

delta-aminobutyl diethoxymethylsilane, and

delta-aminobutyl diethoxyethylsilane.

The alkaline phenolic resin binder solutions that are useful in thepractice of this invention are curable with ester curing agents. Thosewhich are preferred include lactones, organic carbonates, carboxylicacid esters, and mixtures thereof. These species exhibit the esterfunctionality necessary for "ester cure" of the phenolic resin.

Generally, low molecular weight lactones are suitable, such asgamma-butyrolactone, valerolactone, caprolactone, beta-propiolactone,beta-butyrolactone, beta-isobutyrolactone, beta-isopentylactone,gamma-isopentylactone and delta-pentylactone. Carboxylic acid esterswhich are suitable include those of short and medium chain length, i.e.,about C₁ to C₁₀, alkyl mono or polyhydric alcohols with short or mediumlength, i.e., C₁ to C₁₀ carboxylic acids. Specific carboxylic acidesters include, but are not limited to, n-butyl acetate, ethylene glycoldiacetate, triacetin (glycerol triacetate), dimethyl glutarate, anddimethyl adipate.

Of the organic carbonates, those which are suitable include, but are notlimited to, propylene carbonate, ethylene glycol carbonate, glycerolcarbonate, 1,2-butanediol carbonate, 1,3-butanediol carbonate,1,2-pentanediol carbonate and 1,3-pentadiol carbonate.

The binder may also be cured by gassing with an ester functional curingagent such as a low molecular weight carboxylic acid ester, preferablyone of the C₁ to C₃ alkyl formates, including methyl formate and ethylformate. The gassing curing agent is preferably dispersed in a carriergas as a vapor or an aerosol. This carrier gas must be inert in that itshould not react with the alkyl formate curing agent or have an adverseeffect on the curing reaction or other property of the product. Suitablecarrier gas examples include air and nitrogen.

The relative volatility of the alkyl formates facilitate their use asgassing curing agents. This is especially true of methyl formate whichis a volatile liquid having a boiling point at atmospheric pressure ofabout 31.5° C. At ambient temperatures, it is sufficiently volatile thatpassing a carrier gas through the liquid methyl formate gives aconcentrated methyl formate vapor. Ethyl and propyl formates are lessvolatile than the methyl esters having boiling points in the range of54° C. to 82° C. at atmospheric pressure.

The concentration of formate ester in the carrier gas is preferably atleast 0.2% by volume. The total amount of alkyl formate used willtypically be from about 10% to 110%, preferably from 15% to 35% byweight of the phenolic resin solution. The time required for adequategassing depends on the size and complexity of the core or mold and onthe particular resin used. It can be as short as 0.1 seconds but moreusually is in the range of 1 second to 1 minute. The gassing proceduresare described more particularly in U.S. Pat. No. 4,468,359.

The binder solutions of this invention are particularly suited forbonding reclaimed sand. Reclaimed sand is distinguished from new orpristine sand in that it has been recovered from a dismantled foundrymold or core following use in a metal casting process. It is the heatexperienced during the metal casting which is believed to generate thebinder residues that are believed to be responsible for reducing thetensiles of resin-bonded shapes made from the reclaimed sand with estercurable alkaline phenolic resin binders, and that may be the source ofresidual alkalinity.

RAW BATCH FORMULATION

Also within the scope of this invention are raw batch formulationscomprising a binder solution, sand, and a curing agent. At least 40% byweight of the sand used is reclaimed sand, generally 50% to 100%, andpreferably 60% or more. Suitable reclaimed sand and other components forthe raw batch formulation are those described above.

Thus the binder solution in these raw batch formulations preferablycomprises a highly alkaline phenolic resin in solution, applied in anamount sufficient to bind the sand with the adhesive bonding necessaryfor use in making a foundry mold or core. The quantity of the bindersolution is typically in the range of from about 0.5% to 8% by weight ofresin solution, based on the weight of the sand utilized, when thesolids content of the resin solution is from about 33% up to about 47%.Preferred quantities of the binder solution generally fall below about2% by weight of the sand used.

The third component of these raw batch formulations is a curing agentselected from the group consisting of lactones, carboxylic acid esters,organic carbonates and mixtures thereof, which cure the binder atambient temperature. The curing agent is present in an amount sufficientto cure said binder, with preferred concentrations of curing agentfalling within the range of about 10% to 110% by weight, based on theweight of binder solution.

The raw batch formulation may be formed by combining and mixing thesecomponents to provide a substantially uniform mixture. This can beachieved with simple lab batch mixers, high speed continuous mixers orother conventional equipment. Alternatively, the sand and bindersolution may be mixed and formed into a desired shape, and the curingagent introduced in gaseous or vapor form. When the raw batchformulation is completed by gassing a mixture of sand and curable binderwith a curing agent, the curing agent is preferably a C₁ -C₃ alkylformate, used in the quantity of about 10% to 110% by weight, based onthe weight of curable binder solution.

The binder solution in the raw batch formulation has an "effective"solids content of from about 33% to about 47% by weight, based on thetotal weight of the binder solution therein plus any solvent that isadded to the raw batch formulation which dilutes the binder solution.Suitable solvents may be water or an organic solvent which is soluble inwater, such as methanol, ethanol, a glycol, furfuryl alcohol, mixturesof these, and the like.

This "effective" solids concentration for the binder solution can beachieved by utilizing a low solids binder solution or by utilizing ahigh solids binder solution in combination with a separate solvent thatis added and which will reduce the solids content of the bindersolution. Once the dilution solvent and binder solution are added to thesand and mixed, an "effective" solids content of about 33% to about 47%will be realized, and an improvement in bonding properties will berealized over raw batch formulations containing reclaimed sand andbinder solutions at conventional solids contents of above 50% by weight.

PROCESS FOR PRODUCING FOUNDRY CORES AND MOLDS, MAKING EFFECTIVE USE OFRECLAIMED SAND

A raw batch formulation as described above is prepared by combining andmixing sand, a binder solution and curing agent. A dilution solvent canalso be introduced so as to provide the necessary "effective" solidscontent for the binder solution in the raw batch formulation.

The raw batch formulation is then formed into a desired shape prior tocuring. To form the desired shape, all the components of the raw batchformulation, i.e., sand, binder solution and curing agent, can be mixedand subsequently shaped. Alternatively, the sand and binder solution canbe mixed, shaped, and subsequently gassed with an ester functionalcuring agent. The binder hardens and cures at ambient conditions.

EXAMPLES

This invention will now be demonstrated by the following examples. Inthese examples, and elsewhere throughout the specification, all partsand proportions are by weight, and all temperatures are in degreesCelsius, unless expressly indicated otherwise.

EXAMPLE 1 Preparation of Binder Solutions with Low Solids Contents

In this example, binder solutions for evaluation are prepared from acommercially available ester curable alkaline phenolic resin bindersolution, ALpHASET 9000 resin, sold by Borden, Inc. This binder solutionis referred to in these examples as the "Standard Resin 1."

Resin solutions A through E, prepared from Standard Resin 1 by dilution,have different solids contents that are useful in the practice of thepresent invention. Control Resin 1 is a binder solution having a 30.2%solids content, that is below the useful range prescribed for thepractice of this invention.

The ALpHASET 9000 resin binder solution used (Standard Resin 1) had asolids content of about 54% by weight. This resin is obtained by thereaction of phenol and formaldehyde at a phenol:formaldehyde molar ratioof about 1:1.8. The potassium hydroxide:phenol molar ratio for thisresin is about 0.85:1. The resin solution contains gamma-aminopropyltriethoxy silane in the amount of about 0.4% by weight, based on theweight of the resin solution. The Brookfield viscosity of this resinsolution fell within the range of about 100 to 150 cps, as determined bya Model RVF Brookfield viscometer with a No. 1 spindle, at 20 rpm and at25° C.

The quantities of Standard Resin 1 and water used to produce the bindersolutions of Resin solutions A through E and Control Resin 1,respectively, are indicated below in Table 1 along with the resultantsolids contents, all determined by the method described above. To makeResin C, Standard Resin 1 was further diluted with 5.3% by weight, basedon the total weight of the binder solution, of a 40% solution in waterof gamma-aminopropyl triethoxy silane, to achieve a final water contentof 21.1%.

                  TABLE 1                                                         ______________________________________                                        DILUTION OF STANDARD RESIN 1                                                                      Dilution                                                           Standard Resin 1                                                                         Water       % Solids                                               (wt % percent)                                                                           (wt percent)                                                                              Content                                       ______________________________________                                        Standard Resin 1                                                                         100          0           54                                        Resin A    78.9         21.1        42.5                                      Resin B    83.4         16.6        45.6                                      Resin C    78.9         21.1*       46                                        Resin D    77           23          41.3                                      Resin E    70           30          37.6                                      Control Resin 1                                                                          56           44          30.2                                      ______________________________________                                         *Solution contains 5.3 wt. % of a 40% solution of gammaaminopropyl            triethoxy silane.                                                        

These resin solutions are used in subsequent examples to produce testcores.

EXAMPLE 2 Preparation of Additional Binder Solutions with Low SolidsContents

In this example, a binder solution for evaluation was prepared from adifferent commercially available ester curable alkaline phenolic resinbinder solution, BETASET 9500, sold by Borden, Inc. This resin wasprepared by the reaction of phenol and formaldehyde at a molar ratio ofabout 1:2 and at a potassium hydroxide:phenol molar ratio for this resinof about 0.8:1. This resin binder solution contains gamma- aminopropyltriethoxy silane in the amount of about 0.4% by weight. The Brookfieldviscosity of this resin binder solution fell within the range of about75-100 cps as determined by the method described in Example 1. Thisbinder solution had a solids conent of about 57%, and is referred to as"Standard Resin 2."

Resin F, prepared by dilution from Standard Resin 2, represents a bindersolution within the scope of this invention. Resin F was prepared tocontain 77.7 weight percent of Standard Resin 2 solution and 22.3 weightpercent added water. The solids content for Resin F was 44.3%.

Both Resin F and Standard Resin 2 were used in the preparation of testcores in subsequent examples to illustrate some of the preferredembodiments of this invention.

EXAMPLE 3 Preparation of a Binder Solution With a Low Solids ContentWhere the Resin is Condensed With Mixed Alkalis of Sodium and Potassium

In this example, the binder solution was prepared as follows. About 27.3parts by weight phenol was weighed in a three necked flask fitted with astirrer, thermometer and condenser. To this three necked flask wereadded about 14.9 parts by weight of a 50% sodium hydroxide solution inwater. The contents were mixed and following the addition of the sodiumhydroxide, about 34.9 parts by weight of a 50% formaldehyde solution inwater were added over a period of time at 65° C. Once all theformaldehyde was added, the temperature was raised to about 92° C. untilthe viscosity reached 800 cps to 1000 cps. The temperature was thenreduced to about 72° C. to 74° C. and the mixture was reacted furtheruntil a viscosity of about 8000 cps to 9000 cps was obtained.

After this viscosity was obtained, the resin solution was cooled, andabout 14.4 parts of water, 3.8 parts by weight ethanol, and 2 parts byweight of a 50% potassium hydroxide solution in water were added andmixed. While the solution was cooling, about 0.8% by weight of SilaneA-1100 was added. This finished binder solution had a viscosity of about163 cps, as determined by the method used in Example 1, a solids contentof 51% and a gel time of about 9 minutes 40 seconds. This bindersolution is identified in the Examples herein as "Control Resin 2".

Resin G was prepared by diluting Control Resin 2 to form a bindersolution within the scope of this invention. Resin G was comprised ofabout 80% by weight of Control Resin 2 and 20% by weight of added water,and had a solids content of 37.3% by weight.

EXAMPLE 4 Preparation of Test Cores With Reclaimed Sand

This example demonstrates the use of low solids content binder solutionsof the present invention in forming test cores with reclaimed sand, andcompares the tensile strengths of these test cores to those obtainedusing similar resin binder solutions having more customary solidscontent.

In preparing the test cores, a quantity of sand of about 1500 to 2500gms was added to a Hobart Kitchen Aid Mixer for each Test and Controldescribed below. The sand was brought to a temperature of about 25° C.and about 1.5% by weight of a binder solution, based on sand weight, wasadded to the sand and mixed in for about one minute. The binder solutionand sand which were utilized in each Test and Control are described moreparticularly below.

After the mixing in the binder solution, about 25% by weight triacetincuring agent, based on the weight of binder solution used, was added andmixed in for another 40 seconds.

After mixing, the raw batch formulation thus produced was usedimmediately to form standard American Foundrymen Society's 1-inchdogbone tensile briquettes in a Dietert 696 corebox. The cores werecured at room temperature and the samples were broken at the followingapproximate intervals: one hour, two hours, four hours, and twenty-fourours, after the cores were made. Tensile strength measurements were madeusing a Dietert Universal Sand Strength Machine 400-1, fitted with aTensile Core Strength Accessory 610-N. Average values for about 3 to 4tensile strength measurements were determined.

The reclaimed sand used in this example was recovered from foundry moldsand cores that had been used in casting iron or steel. The reclaimedsand contained a binder residue derived from an ALpHASET 9000 resin thathad been cured with triacetin curing agent. The foundry molds or cores,from which the reclaimed sand was obtained, were dismantled after use ina metal casting process by vibrating the mold or core to loosen sand andbreak up any large lumps with a vibratory mill. The free-flowing sandgranules obtained were subjected to dry attrition in a unit produced byRedford Carver Foundry Products, Sherwood, Ore. The sand obtained hadparticle sizes corresponding to an American Foundrymen's Society'sscreen distribution of about 48.7 Grain Fineness and a loss on ignitionvalue (LOI) of 0.80.

To illustrate the processes of this invention, test cores were madeutilizing the reclaimed sand with the binder solutions described inExample 1 as Resin A and Standard Resin 1, to provide Test A and ControlA, respectively. Raw batch formulations and test cores were prepared asdescribed above and the average tensile strength values for these testcores are reported below in Table 2, along with the percentageimprovement observed in tensile strengths of dogbones made in accordancewith the invention (i.e., Test A dogbones). The hour times reported inthe table represent hours after the test cores were made.

                                      TABLE 2                                     __________________________________________________________________________    Solids                                                                        Content                                                                       of the                  Improvement in                                        Binder   Tensiles (psi) Tensiles %                                            Solution 1 hr                                                                              2 hr                                                                             4 hr                                                                              24 hrs                                                                            1 hr                                                                              2 hr                                                                             4 hr                                                                              24 hrs                                     __________________________________________________________________________    Con-                                                                              54   22  30 40  53  --  -- --  --                                         trol-A                                                                        Test-A                                                                            42.5 23  42 52  63  4.5%                                                                              40%                                                                              30% 18%                                        __________________________________________________________________________

The data in Table 2 show that the Text A binder solution, having asolids contents below conventional levels, i.e., below 45%, providedimproved tensile strengths for test cores made from reclaimed sand.

EXAMPLE 5 Preparation of Test Cores With Pristine Sand

This example compares the tensile strength of test cores made using (1)a conventional binder solution and (2) a binder solution having a solidscontent below 45% with pristine sand.

Test cores were prepared in accordance with the method described inExample 4. The pristine sand used was washed and dried and had aparticle size corresponding to an American Foundrymen Society's screendistribution of about 52 Grain Fineness.

The binder solutions used were those described in Example 1 as Resin Aand the Standard Resin 1. They were used to provide Test B and ControlB, respectively. The test cores did not contain any reclaimed sand andas such. This example does not illustrate the present invention, but ispresented for purposes of comparison. Upon obtaining the raw batchformulations in accordance with the procedures of Example 4, test coreswere made and tested as described in Example 4. The average tensilestrength values calculed from the observed values are reported in Table3, with the percent changes (losses) in tensile strengths indicated forthe test cores made utilizing the binder composition of the presentinvention.

                                      TABLE 3                                     __________________________________________________________________________    Solids                                                                        Content                                                                       of the                 Improvement in                                         Binder   Tensiles (psi)                                                                              Tensiles %                                             Solution 1 hr                                                                             2 hr                                                                              4 hr                                                                             24 hrs                                                                            1 hr                                                                              2 hr                                                                              4 hr                                                                              24 hrs                                     __________________________________________________________________________    Con-                                                                              54   55 75  95 123 --  --  --  --                                         trol-2                                                                        Test-B                                                                            42.5 37 50  75  90 -32%                                                                              -33%                                                                              -21%                                                                              -26%                                       __________________________________________________________________________

The data in Table 3 illustrate that lower solids contents in bindersolutions of alkaline phenolic resin binders provide lower and lesssatisfactory tensile strengths for test cores produced from pristinesand.

EXAMPLE 6 Preparing Test Cores With an Alternate Reclaimed Sand

This example illustrates that the improvement in tensile strengthobtained from the binder solutions of the present invention is notlimited to a particular type of reclaimed sand.

Test cores were made utilizing the binder solutions described in Example1 as Resin B, Resin C and Standard Resin 1 to provide Test C, Test D andControl -C, respectively. These test cores were prepared and tested asdescribed in Example 4.

The reclaimed sand was recovered and reclaimed from foundry molds andcores used in casting metal from a different foundry than the reclaimedsand used in Example 4. The binder that had been used in making thesemolds and cores was an Alphaset 9000 alkaline phenolic resin cured withtriacetin.

The sand was mechanically reclaimed from the foundry molds and cores atan American Foundrymen's Society screen size distribution of about 55.2Grain Fineness. It had an LOI of 1.14.

The average values for the tensile strengths of the test cores madeutilizing this reclaimed sand are shown below in Table 4.

                                      TABLE 4                                     __________________________________________________________________________    Solids                                                                        Content                                                                       of the                  Improvement in                                        Binder   Tensiles (psi) Tensiles %                                            Solution 1 hr                                                                              2 hr                                                                             4 hr                                                                              24 hrs                                                                            1 hr                                                                              2 hr                                                                             4 hr                                                                              24 hrs                                     __________________________________________________________________________    Con-                                                                              54   15  23 33  30  --  -- --  --                                         trol-C                                                                        Test-C                                                                            45.6 20  27 --  49  30% 17%                                                                              --  63%                                        Test-D                                                                            46   22  27 40  50  46% 17%                                                                              21% 60%                                        __________________________________________________________________________

The data in Table 4 illustrate that improvements in tensile strength canbe obtained with low solids content binder solutions with reclaimedsands from different sources.

EXAMPLE 7 Preparation of Test Cores with Reclaimed Sand/Pristine SandMixtures

Test cores were prepared with mixtures of reclaimed and pristine sandutilizing binder solutions at low solids contents and at conventionalsolids contents, to illustrate the advantages of this invention whenworking with a mixture of pristine sand and reclaimed sand.

Test cores were made utilizing the binder solution described in Example1 as Resin B and Standard Resin 1 to provide Test E and Control D,respectively. The sand used was an 80:20 mixture of reclaimed:pristinesand. The pristine sand was washed and dried silica sand. These testcores were prepared and tested as described in Example 4.

The reclaimed sand was obtained from a foundry different from the sourceof the reclaimed sand described in Examples 4 and 6. The reclaimed sandwas recovered from foundry molds and cores used in casting iron orsteel. These foundry molds and cores contained a binder residue from anAlphaset 9000 resin binder that had been cured with triacetin, asdescribed in Example 4.

The foundry molds or cores were dismantled after removal of the castingand shaken to remove loose sand particles. The sand was thenmechanically reclaimed. The blend of pristine sand and reclaimed sandhad a size distribution corresponding to an AFS screen distribution ofabout 39.56 Grain Fineness and had an LOI of 0.369.

The average values for the tensile strengths and the percentageimprovements obtained by using the binder solutions of this inventionare reported below in Table 5.

                                      TABLE 5                                     __________________________________________________________________________    Solids                                                                        Content                                                                       of the                  Improvement in                                        Binder   Tensiles (psi) Tensiles %                                            Solution 1 hr                                                                              2 hr                                                                             4 hr                                                                              24 hrs                                                                            1 hr                                                                              2 hr                                                                             4 hr                                                                              24 hrs                                     __________________________________________________________________________    Con-                                                                              54   19  27 35  39  --  -- --  --                                         trol-D                                                                        Test-E                                                                            45.6 28  38 44  43  47% 40%                                                                              25% 11%                                        __________________________________________________________________________

The data in Table 5 illustrate that binder solutions of the presentinvention provide improved tensile strengths for foundry cores or moldsmade from mixtures of reclaimed sand with pristine sand.

EXAMPLE 8 Test Cores Prepared by a Vapor Cure Method

Vapor cured test cores were prepared utilizing curable binder solutionsat low solids contents and at more conventional solids contents, toillustrate that the advantages of the present invention can be realizedwith vapor cure methods.

To prepare the test cores, about 1500-2500 gms of reclaimed sand, asused in Example 4, were added to a Hobart Kitchen Aid Mixer. Thisreclaimed sand was brought to a temperature of about 25° C. Bindersolutions described in Example 2 as Resin F and Standard Resin 2 wereutilized in Test-F and Control-E, respectively. For Test-F, 1.8% byweight resin solution, based on the weight of sand, was added to thesand and mixed for 2 minutes. In Control-E, 1.5% by weight, based on theweight of sand, was added to the sand and mixed for 2 minutes.

When mixing was complete, the reclaimed sand/binder solution mixture wasblown with a Redford Carver Core Blower (a tradename of DependableFoundry Equipment Company, Sherwood, Ore.) using 80 psig air pressurefor 1/2 second into a 3-cavity corebox, for producing Standard AmericanFoundrymen Society's one-inch dogbone tensile briquettes. The coreboxwas then gassed for 5 seconds with methyl formate vapors generated in aCerJet Gas Generator (a trade name of Dependable Foundry Equipment,Sherwood, Ore.). Upon gassing, the cores cured under ambient conditions.Tensile strength measurements were made using a Dietert universal sandstrength machine 400-1, fitted with a Tensile Core Strength Accessory610-N.

Although the quantity of resin used in Test-F was greater than that ofControl-E, the percent resin solids based on sand weight was higher forControl-E (0.855) than for Test-F (0.797).

The average values for the tensile strengths of the test cores made areindicated below in Table 6.

                                      TABLE 6                                     __________________________________________________________________________    Solids                                                                        Content                                                                       of the                  Improvement in                                        Binder   Tensiles (psi) Tensiles %                                            Solution 1 hr                                                                              2 hr                                                                             4 hr                                                                              24 hrs                                                                            1 hr                                                                              2 hr                                                                             4 hr                                                                              24 hrs                                     __________________________________________________________________________    Con-                                                                              57   23  22 26  35  --  -- --  --                                         trol-E                                                                        Test-F                                                                            44.3 27  31 32  49  17.3%                                                                             40%                                                                              18% 40%                                        __________________________________________________________________________

The improvement in tensile strength obtained from the low solids contentbinder solution indicates that the advantages of the present inventioncan be realized where reclaimed sand is utilized in a vapor curemanufacturing procedure.

EXAMPLE 9 Preparing Test Cores Utilizing Binder Solutions at SolidsContents Below 33% by Weight

This example illustrates the lower limits for the solids content ofbinder solutions. A comparison is made of tensile strengths for testcores prepared from binder solutions of the present invention and thosehaving lower solids contents, i.e., below about 33%.

Test cores were made utilizing the binder solutions described in Example1 as Resin D, Resin E and Control Resin 1 to provide Test G1, Test G andControl G, respectively. The raw batch formulations were prepared asdescribed in Example 4 and cured with triacetin. The reclaimed sand usedwas as described in Example 4. Average values for tensile strength wereobtained from 3-4 measured values and are reported in Table 7 below.

                                      TABLE 7                                     __________________________________________________________________________    Solids                                                                        Content                                                                       of the                 % Improvement in                                       Binder    Tensiles (psi)                                                                             Tensiles                                               Solution  1 hr                                                                             2 hr                                                                             4 hr                                                                             24 hrs                                                                            1 hr                                                                              2 hr                                                                              4 hr 24 hrs                                    __________________________________________________________________________    Test-G1                                                                            41.3 20 27 30 45  --  --  --   --                                        Test-G                                                                             37.6 20 32 42 65  --   18.5%                                                                               90%                                                                              44.4%                                    Con- 30.2 13 15 25 32  -35%                                                                              -44%                                                                              -16.6%                                                                             -28.8%                                    trol-G                                                                        __________________________________________________________________________

The data in Table 7 illustrate that the use of binder solutions havingsolids contents as low as 30%-31% by weight have an adverse effect ontensile properties of test cores made with 100% reclaimed sand.

EXAMPLE 10 Preparing Test Cores With Low Solids Content Binder SolutionsMade With Mixed Alkalis

This example illustrates that the advantages of the present inventioncan be realized with binder solutions having resins condensed with amixture of sodium and potassium alkalis. A comparison is made of tensilestrengths for test cores prepared from a binder solution of the presentinvention and a binder at a more conventional solids content.

Test cores were prepared with the resins defined in Example 3 as Resin Gand Control Resin 2 to provide Test H and Control H, respectively. Thereclaimed sand was the same sand described in Example 4. These testcores were prepared and tested as described in Example 4. Averagetensile strength values were obtained from 3 or 4 measurements and arereported in Table 8 below.

                                      TABLE 8                                     __________________________________________________________________________    Solids                                                                        Content                                                                       of the                  % Improvement in                                      Binder   Tensiles (psi) Tensiles                                              Solution 1 hr                                                                              2 hr                                                                             4 hr                                                                              24 hrs                                                                            1 hr                                                                              2 hr                                                                             4 hr                                                                              24 hrs                                     __________________________________________________________________________    Con-                                                                              51   20  22 20  15  --  -- --  --                                         trol-H                                                                        Test-H                                                                            37.3 22  23 32  28  10% 4% 60% 86%                                        __________________________________________________________________________

The data in Table 8 illustrate that improvements in tensile strength canbe obtained wherein the phenolic resin binder is made with a mixture ofsodium and potassium alkalis.

EXAMPLE 11 Preparation of Test Cores With a Two Component BinderSolution

This example demonstrates the use of a two component binder solution informing test cores and the improvements in tensile strength obtainedtherefrom. The reclaimed sand was the same sand described in Example 4.

The two component binder solution in this example comprised (1) StandardResin 1 and (2) an amount of dilution water added to the sand. Thetensile strengths of the cores obtained were compared against test coresobtained from the use of Standard Resin 1 without added dilution water.

The test cores were prepared and tested as described in Example 4. About1.5 weight percent Standard Resin 1 was added to the reclaimed sand forControl I and Test I. In Test I, 0.2 weight percent water, based on theinitial weight of the reclaimed sand, was added to the reclaimed sand asa separate component.

Average tensile strength values were obtained from 3 or 4 measurementsmade for each Control and Test and they are reported below in Table 9.

                                      TABLE 9                                     __________________________________________________________________________    Solids                                                                        Content                                                                       of the                  % Improvement in                                      Binder   Tensiles (psi) Tensiles                                              Solution 1 hr                                                                              2 hr                                                                             4 hr                                                                              24 hrs                                                                            1 hr                                                                              2 hr                                                                             4 hr                                                                              24 hrs                                     __________________________________________________________________________    Con-                                                                              54   33  38 45  60  --  -- --  --                                         trol-I                                                                        Test-I                                                                            46.5 40  53 65  72  21% 39%                                                                              44% 20%                                        __________________________________________________________________________

The data in Table 9 show that improved tensile strengths can be obtainedin test cores where the curable binder solution is comprised of twocomponents and the solids content for the combined components fallsbelow 50% by weight. While water was used as the second component anddiluent in this example, it could as well be a silane solution thatwould be expected to result in a further, incremental improvement intensile strength.

CONCLUSION

In the foregoing specification and in the examples, the binder has beenan aqueous solution of an ester curable alkaline phenolic resin.Comparable results are obtainable where the binder is an acidic orneutral phenolic resin, and the curing agent and a source of alkalinityare added to the resin-sand mix either together or separately. Thesource of alkalinity must render the binder solution alkaline to makeester curing effective.

While the invention has been described in connection with specificembodiments thereof, it will be understood that it is capable of furthermodifications. This application is intended to cover any variations,uses or adaptations of the invention following, in general, theprinciples of this invention and including such departures from thepresent disclosures as come within known and customary practice withinthe art to which the invention pertains.

What is claimed:
 1. A binder composition for binding sand comprisinganaqueous solution of an alkaline phenolic resin that is curable atambient temperature with an ester curing agent selected from the groupconsisting of lactones, organic carbonates, carboxylic acid esters andmixtures thereof, wherein said solution has a solids content in therange of about 33% to about 47% by weight, and wherein at least 40% byweight of said sand is reclaimed sand and said reclaimed sand containsan alkaline resin binder residue, said residue being left on thesurfaces of the reclaimed sand after being previously bonded on a shapeby an ester cured alkaline phenolic resin and recovered from said shapein the form of free-flowing sand granules.
 2. The binder composition ofclaim 1 wherein said solids have a weight average molecular weight (Mw)of from 500 to 2500; a formaldehyde:phenol molar ratio of from 1:1 to3:1; an alkali:phenol molar ratio of from 0.2:1 to 1.2:1; and whereinsaid composition may optionally contain a silane to the extent of 0.05%to 3.0% by weight of said aqueous resin ambient temperature with C₁ -C₃alkyl formates, organic esters formed from C₁ to C₁₀ carboxylic acidsand mono- and polyhydric alcohols, and low molecular weight lactones. 3.The binder composition of claim 1 wherein at least 50% of said sand isreclaimed sand.
 4. The binder composition of claim 1 wherein said solidscontent is in the range of about 35% to about 45%.
 5. The bindercomposition of claim 1 wherein said solution has a Brookfield viscositywithin the range of 15 to 150 cps, at a solids concentration of fromabout 33% to about 47%, wherein the Brookfield viscosity is determinedutilizing a Model RVF Brookfield Viscometer with a No. 1 spindle at 20r.p.m. at 25° C.
 6. A binder composition for binding sand of which about50% to 100% by weight of said sand comprises sand reclaimed frommechanically dismantled foundry molds or cores followed use in castingmetals,said reclaimed sand having a size corresponding to an AmericanFoundrymen's Society's screen distribution of 25 to 140 Grain Fineness,and having an alkaline resin binder residue, said residue being left onthe surfaces of the reclaimed sand after being previously bonded in ashape by an ester cured alkaline phenolic resin and recovered from saidshape in the form of free-flowing sand granules, said foundry molds ofcores being made with an alkaline phenolic resin, cured with a curingagent selected from the group consisting of lactones, carboxylic acidesters, organic carbonates and mixtures thereof, wherein said curablebinder solution has a solids content from about 33% to about 47% byweight, said solids comprising a potassium alkali phenolic resin,wherein the molar ratio of potassium hydroxide:phenol falls within therange of about 0.2:1 to 1:1.2, said potassium alkali phenol formaldehyderesin is obtained by a reaction of phenol and formaldehyde at a ratio ofabout 1:1 to 1:3.0, and wherein said curable binder solution resins havea Brookfield viscosity of 75 to 250 cps, as determined by a Model RVFBrookfield viscometer with a No. 1 spindle at 20 rpm at 25° C., at a 53%to 58% solids content.
 7. The binder composition of claim 6 wherein saidcomposition additionally contains a silane, in an amount effective toincrease the tensile strength of the cured binder composition.
 8. A rawbatch composition for use in making foundry molds and cores comprising amixture of(a) sand, wherein said sand comprises at least 40% by weightreclaimed sand and wherein said reclaimed sand contains an alkalineresin binder residue, said residue being left on the surfaces of thereclaimed sand after being previously bonded in a shape by an estercured alkaline phenolic resin and recovered from said shape in the formof free-flowing sand granules, (b) a binder composition wherein saidbinder composition comprises an aqueous solution of an alkaline phenolicresin that is curable at ambient temperature with an ester curing agentselected from the group consisting of lactones, organic carbonates,carboxylic acid esters and mixtures thereof, wherein said solution has asolids content in the range of about 33% to about 47% by weight, and,(c) a curing agent effective for curing said resin in an amountsufficient to cure said binder composition under ambient conditions inthe shape desired.
 9. The raw batch composition of claim 8 wherein saidsand comprises about 50% to 100% by weight reclaimed sand.
 10. The rawbatch composition of claim 8 wherein the binder composition comprisestwo separate components comprising(1) a solution of alkaline phenolicresin and (2) a solvent for said alkaline phenolic resin, the solidscontent for the components, if combined, falling within the range ofabout 33% to about 47%, based on the combined weight of said twocomponents.
 11. The raw batch composition of claim 10 wherein said twocomponents of the curable binder solution comprise(1) a solution ofalkaline phenolic resin having a solids content of above 50% by weight,and (2) an amount of water sufficient to provide a solids content forsaid components, when combined, in the range from about 33% to about 47%by weight.
 12. The raw batch composition of claim 8 wherein the curablebinder composition contains silane in an amount effective to increasetensile strength of said curable binder when cured.
 13. A raw batchcomposition for use in making foundry molds and cores comprising amixture of(a) sand, (b) a binder composition in an amount of 0.5% to 8%by weight, based on the weight of said sand, and (c) a curing agentselected from the group consisting of lactones, carboxylic acid esters,organic carbonates and mixtures thereof, in an amount ranging from about10% to 110% by weight, based on the weight of said binder solution,wherein from about 50% to 100% of said sand comprises reclaimed sand,said reclaimed sand contains an alkaline resin binder residue left onthe surfaces of the reclaimed sand after being previously bonded in ashape by an ester cured alkaline phenolic resin and recovered from saidshape in the form of free-flowing sand granules having a sizecorresponding to an American Foundrymen's Society's screen distributionof from 25 to 140 Grain Fineness, and wherein said binder compositioncomprises of an aqueous solution of an alkaline phenolic resin curableat ambient temperature by a curing agent having ester functionality,wherein said solution has a solids contents in the range of about 33% toabout 47% by weight and, wherein said alkaline phenolic resin comprisesa potassium alkali phenolic resin which is a reaction product of aphenol and formaldehyde at a phenol:formaldehyde ratio within the rangeof about 1:1 to 1:3.0, wherein said alkaline phenolic resin has analkali phenol molar ratio of 0.2:1 to 1.2:1.
 14. The raw batchcomposition of claim 13 wherein said binder composition comprises asilane in an amount effective to increase the tensile strength of thefoundry molds of cores obtained therefrom.